Expansion of Product_{m>=1} (1+x^m)^21.

Terms

a(0) =1a(1) =21a(2) =231a(3) =1792a(4) =11067a(5) =58002a(6) =268093a(7) =1120899a(8) =4315269a(9) =15497986a(10) =52441347a(11) =168487473a(12) =517184185a(13) =1524390777a(14) =4332440454a(15) =11914441196a(16) =31798680774a(17) =82574231187a(18) =209091601271a(19) =517272712845